Constantin Stanislavski was a Russian theatre practitioner born in 1863 who developed influential acting techniques known as the Stanislavski system. He founded the Moscow Art Theatre in 1898, pioneering psychological realism and departing from the stylized acting of the time by encouraging actors to immerse themselves in their characters. His system and teachings spread internationally through his students and books, profoundly shaping actor training and modern theatre. He emphasized imagination, physical action, given circumstances, and understanding a character's inner motivations to create believable performances. Though some found his methods stressful, Stanislavski had a revolutionary impact on realistic acting around the world.